In a conventional gun, acceleration of a projectile to muzzle velocity is achieved solely by combustion of a propellant charge detonated in the gun breech. Traditionally the breech propellant charge has been in a solid form. Considering the advanced protective armor carried by state-of-the-art military tanks, tank guns, to be effective against such tanks, must generate muzzle energies in the range of 12-14 Mega-Joules to accelerate, for example, a 120 mm projectile weighing 7.12 Kg. to a muzzle velocity of 2000 m/sec. This is a tall order for existing gun steel and solid propellant technologies.
Emerging liquid propellant technology offers great promise for increasing muzzle energies and velocity for enhanced armor-piercing capabilities. One approach to boosting muzzle velocity is to equip the projectile with a travelling liquid propellant charge that is detonated as the projectile is propelled down the gun bore by a primary or main propellant charge detonated in the breech of the gun. The down-bore combustion of the travelling charge introduces increasing gas pressures in the bore aft the projectile as the pressurized gases generated by the combusting breech propellant charge are expanding and losing intensity. Muzzle velocities approaching 3000 m/sec. have been achieved using this liquid propellant travelling charge approach exemplified in Bulman, U.S. Pat. No. 4,993,309, for example.
The travelling charge approach, although effective in boosting the muzzle velocity, presents significant challenges that have yet to be overcome. Lack of repeatability and burst fire accuracy are persistent problems, since it is difficult to consistently achieve detonation of the travelling charge at a precise down-bore location on a shot-to-shot basis. The weight of the travelling charge adds to the mass that is to be accelerated down the bore, and thus the contribution of the breech charge to the projectile muzzle velocity is diminished. In addition, when using a travelling charge, a special separator is required to isolate the travelling charge from the breech charge when the latter is detonated to launch the projectile down-bore. Moreover, the presence of the travelling charge complicates loading of the projectile into the breech and ramming it into the forcing cone of the gun barrel.